1. Field of the Invention
The invention relates to a liquid supply method in a liquid-jet apparatus.
2. Description of the Related Art
A serial inkjet recording apparatus typically includes a carriage that scans in a main scanning direction perpendicular to a sheet transfer direction, and the carriage includes a liquid-jet head having plural nozzles to jet liquid toward a sheet. One of methods for supplying ink to the liquid-jet head includes supplying ink from an ink cartridge to the liquid-jet head. The other method may include temporarily supplying ink from the ink cartridge fixed to a predetermined position to a head tank arranged above the liquid-jet head via a liquid supply tube, and transferring the ink temporarily supplied in the head tank to the liquid-jet head communicating with the head tank.
In the liquid-jet head, ink pressure in the nozzles may preferably be adjusted in a range of −0.2 to −1 kPa for jetting appropriate ink droplets. As already described, the liquid-jet head is communicating with the head tank. Accordingly, meniscus pressure, which is pressure near nozzle interfaces of the nozzles in the liquid-jet head, may be controlled by adjusting an internal pressure of the head tank. Japanese Patent Application Publication No. 2005-59490 (hereinafter referred to as “Patent Document 1”) discloses an example of a head tank configuration that is capable of adjusting the internal pressure of the head tank. The head tank disclosed in Patent Document 1 includes a flexible member. The head tank disclosed also includes an elastic member that extends slightly longer than its natural length when introducing ambient air into the head tank and applies a bias to the flexible member in a direction from inside to outside of the flexible member when the head tank is at a negative pressure.
An ink supply method for the head tank disclosed in Patent Document 1 is described in detail below. As described above, since the head tank disclosed in Patent Document 1 is formed of the flexible member, the flexible member gradually expands and deforms as ink is supplied to the head tank to increase an ink volume inside the ink tank. That is, when the head tank is filled with the ink (i.e., when the head tank is full), the head tank formed of the flexible member is fully expanded by introducing ambient air, and ink is supplied to the fully expanded head tank. After the head tank is filled with ink, the head tank is enclosed or shielded. Thereafter, when the nozzles of the liquid-jet head communicating with the head tank jet several ink droplets, the entire ink volume is reduced in an amount corresponding to the amount of the ink droplets jetted from the nozzles of the liquid-jet head. With the reduction of the entire ink volume, the head tank formed of the flexible member may spontaneously shrink. However, the elastic member prevents the flexible member from shrinking by the application of the bias to the flexible member as described above. Accordingly, the liquid-jet head and the head tank communicating with the liquid-jet head include an initial negative pressure.
The ink volume inside the head tank is reduced while ink is consumed by jetting ink droplets from the liquid-jet head, and the head tank formed of the flexible member deforms in a direction from the outside to the inside of the head tank. In this process, since the elastic member applies the bias to the flexible member in a direction from the inside to the outside of the head tank formed of the flexible member, the negative pressure inside the head tank and the liquid-jet head obtained by jetting ink droplets after cancellation of the ambient air introduction may be adjusted in a range in which the liquid-jet head is capable of jetting ink droplets.
Further, in the head tank configuration disclosed in Patent Document 1, a lever is attached to the head tank formed of the flexible member such that a remaining amount of ink in the head tank is detected by detecting a position of a pointed end of the lever. The lever is attached to the head tank formed of the flexible member capable of generating a negative pressure inside the head tank, and hence the lever is hereinafter called a negative pressure lever. The position of the negative pressure lever is detected either by its home position or by a negative lever position detecting sensor provided near a maintenance-restoration section that restores a nozzle jet function by suctioning remaining ink (liquid) inside the nozzles of the liquid-jet head or cleaning a periphery of the nozzle face of the liquid-jet head. In the head tank configuration disclosed in Patent Document 1, the position of the negative pressure lever when the initial negative pressure is generated inside the head tank and the position of the negative pressure lever when the head tank is filled with ink are detected, and information on such detected positions of the negative pressure lever is stored in advance. In the head tank configuration disclosed in Patent Document 1, when printing is continuously carried out, an amount of ink to be jetted based on liquid-jet signals may be estimated in advance. If an estimated value corresponding to the cumulative amount of ink jetted reaches a threshold indicating that ink needs to be supplied to the head tank, the printing is temporarily interrupted and ink is supplied to the head tank without introducing an ambient air until the position of the negative pressure lever returns to the stored position detected by the negative pressure lever detecting sensor when the initial negative pressure is generated inside the head tank.
However, in the head tank configuration disclosed in Patent Document 1, the amount of ink to be jetted based on the liquid-jet a signal is estimated in advance. If the estimated value corresponding to the cumulative amount of ink to be jetted reaches a threshold indicating that ink needs to be supplied to the head tank, the printing is temporarily interrupted. Then, the carriage is returned to the home position or to a position of the maintenance-restoration section where the negative pressure lever detecting sensor is provided for detecting the position of the negative pressure lever. Thereafter, ink is supplied to the head tank until the position of the negative pressure lever returns to the initial position of the negative pressure lever detected by the negative pressure lever detecting sensor when the initial negative pressure is generated inside the head tank. As described above, with the head tank configuration disclosed in Patent Document 1, the printing may not be restarted until the negative pressure lever detecting sensor detects via the negative pressure lever that the head tank is filled with the ink. Thus, printing duration in total may become longer because the printing duration includes traveling time for the carriage traveling for detecting the negative lever position, detecting time for the amount of ink supplied, and ink supply time for supplying ink to the head tank until the head tank is filled with ink.